Method and lightweight composition for sealing pipe and wellbores

ABSTRACT

The present invention provides a method and composition for sealing pipe in wellbores. The composition includes cement, water, gel and laminate particles. The laminate particles are added in a proportion to the cement to provide a weight to the slurry of between 12.5-14.5 pounds per gallon. The cement slurry is pumped down through pipe, such as casing, into the annulus and back up towards the surface. The cement slurry can extend from the producing formation to a location above the producing formation to form a seal. By utilizing the light weight cement slurry, the pipe such as casing can be sealed in a single stage operation.

This application claims the benefit of U.S. provisional application Ser. No. 60/787,301, filed Mar. 30, 2006.

FIELD OF THE INVENTION

The present invention provides methods of using low density cement slurry compositions to seal and protect pipe in a wellbore in a conventional oil and gas well.

BACKGROUND OF THE INVENTION

Oil and gas wells have been drilled in much the same way for over a century. A drilling rig bores a hole from the surface until the wellbore either intersects desirable hydrocarbon formations or reaches a predetermined depth. During drilling operations, pipe or casing is inserted into the wellbore through which the recovered hydrocarbons are intended to flow, either directly, or internally through tubing, upward to the earth's surface. This casing is made of steel and may extend downward from the surface thousands of feet.

A typical wellbore penetrates numerous formations and encounters highly corrosive fluids, extreme temperatures, as well as high pressures. The casing and wellbore, if left unprotected, are subject to undesirable movement, corrosion, and erosion.

To protect the casing and wellbore from such movement and damage, a cement slurry is pumped into the annulus between the outer surface of the casing and the wellbore walls. This is accomplished by hydraulically pumping this slurry downward from the surface through the casing. Upon reaching the lowermost point of the casing, the slurry exits radially though a float shoe and enters the annular space between the casing and the wellbore walls. The slurry then begins to travel upward towards the surface to the desired geologic level. This slurry, upon hardening, and if properly prepared, stabilizes the position of the casing within the wellbore and protects the casing from the corrosive effects of fluids found in zones through which the well is drilled. The slurry bonds to the surface of the casing, and penetrates small cracks and fissures within the walls of the wellbore. If corrosive fluids or elements are allowed to reach the casing, the integrity of the pipe and, consequently, the production of the well, can be severely impacted. Such damage requires expensive and time consuming repair efforts which severely lower the overall profitability of the well. In addition, the cement slurry, once hardened, forms a seal that prevents fluids from migrating between zones or formations penetrated by the wellbore.

DESCRIPTION OF THE PRIOR ART

Most oil and gas drilling producers use two different types of cement slurry compositions when sealing casing. Traditionally, the type chosen depends upon the area of the wellbore intended to be sealed. These areas can be fairly categorized as either “producing zones” or “areas above the producing zones.” Producing zones are typically found at the lower depths of the wellbore. Oil and gas producers have a great economic interest in fully protecting the casing and wellbore in these areas. To protect the producing zone, the producer uses a high density, heavy cement slurry, which has a high compressive strength. This high density cement slurry, generally weighing between fourteen and sixteen pounds per gallon, is typically comprised of a Type C or H Portland cement and a combination of additives such as sand, plaster of Paris, gel, potassium chloride, pozzolan, and crushed melamine based particles. Some of these additives provide a physical barrier to migrating fluids and reduce permeability of the cement. In the areas above the producing zones, a light weight, low density cement slurry is generally used since the use of high density, heavy cement above the producing zones creates excessive amounts of hydrostatic pressure which can fracture the producing zone, possibly causing damage to the formation.

The conventional method of pumping cement slurry into the producing area of the wellbore is a multi-step process, in order to protect the producing zone or zones. First, the high density cement slurry is pumped through the casing and out a float shoe into the annulus to a level above the uppermost producing zone. Then a multi-stage cementing bomb is dropped down the casing to actuate the multi-stage cementing tool (DV tool) at the designed depth in the casing for two-staging the cement job, and typically at a level only a few hundred feet above the uppermost producing zone and the top of the first stage, high density cement slurry. The DV tool has a moveable, sliding sleeve that when moved downward by hydraulic pressure exerted on the bomb, exposes port holes or perforations extending through the wall of the casing. These perforations allow the operator to perform the step of circulating drilling mud in the annulus above the producing zones for several hours to maintain the integrity of the wellbore while the heavy cement below hardens or sets. After the heavy cement sets, the operator pumps the low density, second-stage cement slurry down through the casing, out of the DV tool perforations, and up into the annulus between the casing and the wellbore wall. This multi-step process for cementing the casing is time consuming and laborious.

Light weight, low density cement slurry can be pumped to great depths and returned to a predetermined point in the annulus. In many wells, a light weight cement slurry can be returned more than 6000 feet above the float shoe. However, conventional light weight slurries and application methods do not provide necessary stability and protection to the upper regions of the primary casing and wellbore. To accomplish this, the low density slurry must be both light weight and contain elements that offer protection against pressure, heat, and corrosive fluids.

To decrease the weight of a cement slurry, its density must be reduced. To lower the density of the slurry, water is often added. However, the added water has the undesirable effects of diminishing the strength of the hardened cement, as well as increasing its overall permeability. One method of reducing the density of the slurry while maintaining desirable strength and permeability characteristics is to add silica. Chatterji U.S. Pat. No. 6,367,549 teaches that silica, when added to a conventional cement slurry, can help maintain strength and decrease permeability. However, the addition of silica has proved to be a time consuming and unsatisfactory method of preparing a low density cement slurry needed in the upper regions of the wellbore. Thus, there are needs for improved methods for sealing casing in wellbores.

SUMMARY OF THE INVENTION

The present invention provides a method of sealing pipe in a wellbore that penetrates a formation. A cement slurry comprised of cement, water, gel and laminate particles is provided. The cement slurry is located in the annulus around the pipe. The cement slurry is allowed to harden.

In accordance with one aspect of the present invention, the step of providing a cement slurry further comprises the step of providing the cement slurry at a weight of 12.5-14.5 pounds per gallon.

In accordance with another aspect of the present invention, the step of providing a cement slurry further comprises providing a ratio of laminate particles to cement of 4:94 to 8:94 by weight.

In accordance with still another aspect of the present invention, the step of providing a cement slurry further comprises providing laminate particles of 25-2000 microns in size.

In accordance with still another aspect of the present invention, the step of locating the cement slurry further comprises the step of locating the cement slurry in the annulus at the formation and above the formation in order to provide a seal and to protect the pipe from corrosive fluids in the wellbore.

In accordance with still another aspect of the present invention, the cement slurry is a first cement slurry and is located in the annulus above the formation. A second cement slurry that is heavier than the first cement slurry is located in the annulus at the formation.

In accordance with still another aspect of the present invention, the second cement slurry has a weight of 14 to 16 pounds per gallon.

In accordance with still another aspect of the present invention, the second cement slurry further comprises laminate particles.

The present invention also provides a wellbore having a pipe that penetrates a formation, with the pipe having an annulus. A sealing composition located in the annulus is used to seal the pipe in the wellbore. The sealing composition comprises cement, water, gel and laminate particles.

In accordance with one aspect of the present invention, the cement is selected from the group containing Type C or Type H Portland cement.

In accordance with another aspect of the present invention, the sealing composition forms a slurry having a weight of 12.5-14.5 pounds per gallon.

In accordance with still another aspect of the present invention, the ratio of laminate particles to cement is 4:94 to 8:94 by weight.

In accordance with still another aspect of the present invention, the laminate particles are sized between 250-2000 microns.

In accordance with still another aspect of the present invention, the cement slurry extends in the annulus from the formation to a location above the formation so as to protect the pipe from corrosive fluids.

In accordance with still another aspect of the present invention, the cement slurry is a first cement slurry and is located in the annulus above the formation. A second cement slurry that comprises cement, water, gel and laminate particles, is located in the annulus at the formation. The second cement slurry is heavier than the first cement slurry.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional side view of a wellbore with casing extending through various geologic formations illustrating the method of the present invention, in accordance with a preferred embodiment.

FIG. 2 is a cross-sectional side view of a wellbore illustrating the method of the present invention in accordance with another embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, the present invention provides for sealing and protecting pipe in a wellbore. A pumpable sealing composition is used. Referring to FIG. 1, a cross-sectional, side view of a wellbore 6 and casing 2, 5 is shown. The wellbore 6 is drilled by means of a drilling rig 1 on the earth's surface 3. The wellbore 6 penetrates various formations and zones, including corrosive fluid zones 4, and the producing zones 8. A surface casing 2 and primary casing 5 are inserted into the wellbore 6. Attached to the last joint of the primary casing 5 string is a float shoe 9. The float shoe 9 is a tapered, often bullet-nosed device fitted with a check valve, which prevents reverse flow, or U-tubing, of the cement slurry 7 from the annulus into the casing 2.

The method provided by the preferred embodiment of the present invention will now be described. A low density, light weight cement slurry 7 is provided. This low density, light weight slurry is comprised of cement, water, gel and laminate particles of various sizes, which slurry may be applied to the zones 4 and 8 in a single operation.

Various types of cement can be used. Preferably, Portland cement is used. In the preferred embodiment, the Portland cement is Type C or H Portland cement. The cement can be nonexpanding or expanding. Expanding cement typically contains plaster of Paris.

The amount of water is an operable amount to not only make the cement react and set (or harden), but also to regulate the density of the cement slurry. Any water that rises to the top of a cement sample in the first two hours after a sample of the cement mixture is caught is known as free water. For example, for a cement slurry of 13.1 pounds per gallon, 10 gallons of water is added to each sack of cement (a sack contains 94 pounds of cement). For a heavier slurry of 14 pounds per gallon, 7 gallons of water per sack of cement is used. Thus, at least 3 gallons of water is free water in the example unless a gelling agent is added.

Gelling agents, or extenders, are added to tie up the free water and prevent the slurry from being too thin and runny. As an example, up to 6% (by weight of cement) of bentonite is used. As another example, up to 2% (by weight of cement) of sodium metasilicate is used. Other gelling agents can also be used to tie up the free water and keep it from coming out of the slurry while the cement sets up or hardens.

The laminate particles are made of various components. In the preferred embodiment, the laminate particles are made of thermoset laminate ground into particles of various sizes. The laminate can be of the type used in countertop surfaces. In fact, the laminate particles are typically made from laminate which has been discarded or rejected and is therefore unusable for use as a countertop surface. The laminate is made of paper, melamine and phenolic resins. The general composition is believed to be 72% cellulose paper, 19% phenolic resin and 9% melamine resin. The laminate particles are conventional and commercially available under the trademark Pheno Seal®. Typical particle sizes are, in percent retained:

Mesh Micron Fine Medium Coarse −80 177 1.6 0 0 +80 177 4.0 0 0 +60 250 44.9 0.1 0 +20 850 20.6 0.2 0.2 +14 1190 28.9 25.4 12.4 +10 2000 0 74.3 82.2 +4 4750 0 0 5.2

Some of the particles can be as large as thumbnail size (about 12,000 microns).

The small, or fine, particles seal the pores in the formations along the well bore. The larger size, or coarse, particles, such as chip size, provide flexibility to the cement after hardening and can seal off fractures in the formation, both naturally occurring fractures or induced fractures during the drilling or cementing operation. Various combinations of the particle sizes can be used. For example, the laminate particles can be all fine, or all medium, or all coarse, or a mixture of two or all three. As another example, the laminate particles can be ⅓ fine, ⅓ medium and ⅓ coarse. In practice laminate particles of medium sizes is used most often.

In the preferred embodiment, the laminate particles are mixed with Type C Portland cement at a ratio ranging from 4:94 to 8:94. Thus, for every ninety-four pounds (or a sack) of Portland cement, four to eight pounds of laminate particles are added. The weight of the light weight slurry ranges from approximately 12.5 to 14.5 pounds per gallon. In the preferred embodiment, eight pounds of laminate particles are added. The cement, water, gel and laminate particles are mixed in conventional cement mixers.

Additives such as potassium chloride, retarders, pozzolon, and plaster of Paris may also be added along with many others. The weight of the low density light weight cement slurry, when properly mixed in accordance with the preferred embodiment, is approximately 13.1 pounds per gallon. A 13.1 lb. per gallon cement slurry prepared in this manner possesses desirable high strength and low permeability characteristics, suitable for sealing casing the entire length of the wellbore 6.

Many loss of circulation additives can be mixed along with the laminate particles to enhance the cement, but are not necessarily needed. One such additive is fiberglass particles. The particles are ground fiberglass pieces, which pieces have glass fibers and resin. The amount of the laminate particles can be reduced by adding fiberglass. For example, in place of using eight pounds of laminate particles, the cement slurry would have four pounds of laminate particles and four pounds of fiberglass. The amount of fiberglass used can vary. However, it is preferred that the amount of laminate particles be kept at or above 50% relative to the fiberglass particles. That is to say for the example given, no less than four pounds of laminate particles be used. The amount of laminate particles can vary relative to fiberglass particles between 50-100%. In the example given above, this is between 4-8 pounds.

The low density light weight cement slurry 7 is pumped down the casing 2, 5 and through the float shoe 9 into the annulus, and then back up the annulus toward the surface 3. Because the cement slurry 7 of the preferred embodiment is light weight, this slurry 7 may be pumped up the annulus from the float shoe 9 farther than is possible with traditional cement slurries. The cement slurry can be pumped up to the surface through the annulus. My experiments have shown that the cement slurry can be pumped 6000 feet above the production zones in the annulus in one, continuous stage.

If the formation in the producing zone 8 should fracture under the weight of the cement slurry 7, the laminate particles seal the cracks in the zone.

The cement slurry 7 is allowed to harden. The cement slurry 7 is left undisturbed for a period of time in order to harden. While hardening, circulation can be maintained in the annulus above the cement slurry, if the cement slurry does not extend to the surface. Circulation can be maintained in accordance with conventional practice, such as with a DV tool.

The method provided by the preferred embodiment allows the light weight cement slurry 7 to seal not only the areas above the producing zones 8, but the producing zones 8 as well. The method provided has the advantage, as compared to traditional methods of sealing primary casing 5 in a wellbore 6, in that the light weight slurry 7 can be inserted in virtually the entire length of the wellbore 6, in a single operation.

Although the method of pumping the light weight, low density cement slurry in accordance with the preferred embodiment involves pumping the slurry 7 through the casing 5, the slurry 7 can also be pumped directly down the annulus from the surface.

Conventional cementing operations utilize a multi-step, time consuming process of pumping high density cement slurry, typically with a weight of fourteen to sixteen pounds per gallon in the first stage, then opening the multi-stage cementer casing perforations above the producing zones and circulating drilling mud for several hours allowing the first stage cement to harden before pumping the second stage cement. Finally the second stage, low density cement slurry is pumped through the multi-stage cementer perforations into the annulus and displaced with a wiper plug to the DV tool thereby completing the cementing operation.

In contrast, the method provided by the present invention allows the entire sealing, cementing operation to take place in a single stage. By eliminating the steps of pumping the high density slurry, opening the perforations in the DV tool, and circulating drilling mud, the operator saves time, money, and equipment.

In accordance with another embodiment, two different cement slurries can be pumped downhole around the casing in one operation. Referring to FIG. 2, first a quantity of the light weight cement slurry 7 is pumped downhole. This is followed by a quantity of heavier cement slurry 10. The heavier cement slurry weighs 14-16 pounds per gallon. The heavier cement slurry includes cement, water, gel and the laminate particles. Other additives can be provided as well, such as salt, extenders, etc. The cement slurries 7, 10 are pumped down through the casing, out through the float shoe 9, and then up into the annulus. After pumping, the heavier cement slurry 10 extends from the bottom of the casing to a location above the uppermost production zone 8, while the light weight cement slurry 7 extends from the heavier cement 10 up toward the surface 3 for a desired distance. This embodiment allows the entire cementing operation to occur in a single stage. The zones 8 are protected by a higher compressive strength sealing composition 10, while the casing above the zones 8 is protected from corrosive fluid by the lightweight sealing composition 7.

The foregoing disclosure and showings made in the drawing are merely illustrative of the principles of this invention and are not to be interpreted in a limiting sense. 

1. A method of sealing pipe in a wellbore that penetrates a formation, comprising the steps of: a) providing a cement slurry comprised of cement, water, gel and laminate particles; b) locating the cement slurry in an annulus around the pipe; c) allowing the cement slurry to harden.
 2. The method of claim 1 wherein the step of providing a cement slurry further comprises the step of providing the cement slurry at a weight of 12.5-14.5 pounds per gallon.
 3. The method of claim 1 wherein the step of providing a cement slurry further comprises the step of providing a ratio of laminate particles to cement of 4:94 to 8:94 by weight.
 4. The method of claim 1 wherein the step of providing a cement slurry further comprises the step of providing laminate particles of 250-2000 microns in size.
 5. The method of claim 1 wherein the step of locating the cement slurry further comprises the step of locating the cement slurry in the annulus at the formation and above the formation in order to provide a seal and to protect the pipe from corrosive fluids in the wellbore.
 6. The method of claim 1 wherein: a) the step of locating the cement slurry further comprises the step of locating the cement slurry, which is a first cement slurry, in the annulus above the formation; b) locating a second cement slurry that is heavier than the first cement slurry in the annulus at the formation.
 7. The method of claim 6 wherein the step of locating a second cement slurry further comprises the step of providing a second cement slurry having a weight of between 13.5 to 16 pounds per gallon.
 8. The method of claim 6 wherein the second cement slurry further comprises laminate particles.
 9. The method of claim 1 wherein: the step of providing a cement slurry further comprises the steps of providing laminate particles of 250-2000 microns in size, the cement slurry having a weight 12.5-14.5 pounds per gallon and the ratio of laminate particles to cement being in between 4:94 to 8:94 by weight.
 10. In a wellbore having a pipe that penetrates a formation, the pipe having an annulus, a sealing composition for use in the sealing of the pipe in the wellbore, comprising: cement, water, gel and laminate particles, the sealing composition located in the annulus.
 11. The wellbore of claim 10 wherein the cement is selected from the group containing Type C or Type H Portland cement.
 12. The wellbore of claim 10 wherein the sealing composition forms a slurry having a weight of 12.5-14.5 pounds per gallon.
 13. The wellbore of claim 10 wherein the ratio of laminate particles to cement is 4:94 to 8:94 by weight.
 14. The wellbore of claim 10 wherein the laminate particles are sized between 250-2000 microns.
 15. The wellbore of claim 10, wherein: a) the sealing composition forms a slurry having a weight of 12.5-14.5 pounds per gallon; b) the ratio of laminate particles to cement is 4:94 to 8:94 by weight; c) the laminate particles are sized between 250-2000 microns.
 16. The wellbore of claim 10 wherein the cement slurry extends in the annulus from the formation to a location above the formation so as to protect the pipe from corrosive fluids.
 17. The wellbore of claim 10 wherein the cement slurry is a fist cement slurry and is located in the annulus above the formation, further comprising a second cement slurry that comprises cement, water, gel and laminate particles, the second cement slurry, being heavier than the first cement slurry, the second cement slurry being located in the annulus at the formation. 